Validate Functions (for Clickhouse)

[archiewood]

We're exploring using this to do browser based SQL validation without sending queries to Clickhouse in https://evidence.dev

For this we would need to be able to validate functions.

Open to PRing in if this makes sense for your project

[tobilg]

Hi! PRs are always welcome! It's an early version currently, and I was focussing on getting the sqlglot fixtures to work, so it think there's probably a lot of room for improvement. Feel free to create a PR! Thanks!